Tension mechanism for sewing-machines.



R. K. HOHMANN.

TENSION MECHANISM FOR SEWING MACHINES.

APPLICATION FILED SEPT. 18, I912. 1,198,545.

Patented Sept. 19, 1916.

PF--. a /mw UNITED STATES PATENT OFFICE.

RICHARD K. HOHMANN, OF SAN DIEGO, CALIFORNIA.

TENSION MECHANISM FOR SEVJING-MACHINES.

Specification of Letters Patent. Patented Sept. 19 1916 Application filed September 18, 1912. Serial No. 721,039.

To all whom it may concern Be it known that I, RICHARD H. Horr- MANN, a citizen of the United States, and resident of San Diego, county of San Diego, State of California, have invented certain new and useful Improvements in Tension Mechanism for Sewing-Machines, of which the following is a specification.

This invention relates to a mechanism for regulating the tension on the thread in sewing machines. It has been my purpose tomake a simple and efiicient tension device and one which will automatically change the pressure on the thread and, consequently, the resistance to its movement in accordance with the size of the thread used.

The novel features of the invention will be apparent from the following description taken in connection with the drawings.

In the drawings Figure 1 is a front view of the face plate of a sewing machine having my tension device in place; Fig. 2 is a vertical section through a part of the face plate at the point where my tension device is located, but most of the elements of that device are omitted from this figure; Fig. 3 is a perspective view partly broken away showing the bushing on which the tension plates are threaded; Fig. 4 is a perspective view of a shaft which passes through the bushing so as to beoperatively connected to one of the tension plates; Fig. 5 is a cross section on the line 5-5 of Fig. 3; Fig. 6

is an edge view of the two tension plates one of them being in section; Fig. 7 is a perspective View of a washer which fits on the bushing against one of the plates; Fig. 8 is an edge view partly in section showing the retaining cap for the tension plates; Fig. 9 is a face view of a leaf spring for applying pressure to the plates; and Fig. 10 is a vertical section on the line 10-10 in Fig. 1.

As shown in these drawings, 1 represents the face plate of a sewing machine which carries at its top the thread check 2 and on its face the thread guides 3, 4 and 5, the auxiliary spring 6 being provided at the guide 4.

7 represents the take-up arm and 8 represents my tension mechanism.

It has been found in actual practice that the pressure on the tension plates of a sewing machine which will produce the necessary tension where a small thread is being used will not be sufficient where a larger thread is used, and therefore, to secure proper and effective action it is necessary to increase the pressure on the plates as the size of the thread increases, and it has been found that the compression of a spring as the plates separate will not be sufficient to give enough increased pressure to serve the purpose. It will be understood that with a large thread a stronger pull is required in forming the loop and drawing it up tight and this is what makes greater tension necessary with large thread. According to my present invention the tension device is set in such a way that the pressure on the plates is just that necessary for use with small thread and the construction is such that if the plates are separated by the admission of a larger thread they will bring into action an additional means tending to press them together and thus a greater pressure will be exerted on the large thread than on the small thread without the necessity for manipulation or change in the tension mechanism. In other words, the action is automatic.

In the particular form of the tension mechanism a circular disk 9 is secured to the face plate 1 and it has a central opening 10 and a circular recess 11 on its face. The tension disk 12 fits in the circular recess 11 and it is provided with a central opening 13 larger in diameter than the opening 10. The tension plate 14 is similar to the plate 12 having a similar central opening and the faces of these two plates which meet are rounded at the outer edge, as shown, so as to admit the thread easily between them. A bushing 15 which is in the general form of a hollow cylinder passes through the openings in the plates 12 and 14 and through the opening 10 fitting the said opening 10- closely, but capable of longitudinal movement therein. Near the outer end the bushing 15 is enlarged whereby a circular shoulder 16 is formed and this shoulder fits against the outer face of the part 9, this shoulder serving as a stop to limit the inward movement of the bushing 15 through the opening 10. The two tension plates 12 and 14 fit around and are threaded on the enlarged end 17 of the bushing 15, but the combined thickness of these two plates is not quite as great as the length of the enlarged end so that as far as the bushing is concerned, the plates rest loosely on it and are capable of some separation without disturbing the bushing. A flange 18 is, however, provided on the outer end of the enlarged portion 17 and the plate 14: is adapted to strike against this flange as it is separated from the plate 12 a definite distance. A washer 19 has a central opening 20 which opening is partially circular in form, but which has straight sides and which fits closely around the flange 18, and while it cannot turn on that flange, it can move thereon longitudinally of the bushing. A retaining cap 21 which is provided for convenience with a knob 22 fits against the washer 19 and it preferably has a recess 23 on its face to receive that washer and the central recess 24. to receive the end of the bushing 15 including the flange 18.

A shaft 25 passes longitudinally through the bushing 15 and has a screw threaded end fitting in the opening 26 in the retaining cap and consequently it moves with the cap. A coil spring 27 surrounds the shaft 25 fitting at one end against the enlarged portion 28 and at the other end bearing against the shoulder 29 formed at the outer end of the bushing 15 where the diameter of the central opening is reduced to practically the size of the shaft 25. The enlarged end 28 has projecting therefrom a pin 30 working in the slot 81 in the bushing whereby the shaft can move longitudinally, but cannot turn in the bushing. A leaf spring 32 is secured to the inner face of the face plate 1 by suitable means such as the screw 83 and the free end of this spring is forked at 34 as shown in Fig. 9. The forked end of this spring fits over the inner end of the bushing 15 engaging the vertical slots 35 in that bushing and thus the bushing cannot be moved longitudinally without bending the spring.

From the above described construction it will be observed that where a small thread is inserted between the plates 12 and 14 those plates will separate and the effect of the first separating movement will be to compress the coil spring 27 by pulling the shaft 25 longitudinally through the bushing. This pulling action will, of course, take place through the plate 14, the washer 19, the cap 21 and the shaft 25. Since the plate 14; is separated a slight distance from the flange 18 it will not disturb the bushing until it has separated from the plate 12 sufiiciently far to come in contact with the flange 18. This distance is made sufficient to admit small thread to the tension device so that the only tension on said small thread will result from the pressure of the spring 27 and the strength of that spring is made and regulated so as to produce the proper and desired tension on such small thread. When,

however, a larger thread is placed between the plates the plate 14 will engage the flange 18 and in separating further will necessarily draw the bushing 15 with it, this bushing being held by the leaf spring 32 which is constantly under tension tending to pull the bushing in. It will be observed that the pressure on the thread when the bushing 15 is moved will be considerably greater than when the spring 27 alone is acting. The spring 32 may be made stronger than the spring 27, and its action is added to the ac,- tion of the spring 27. By this construction the added pressure on the thread is brought about automatically by the size of the thread itself since the additional pressing means is brought into action by the separation of the disks as the thread enters between them.

Having described my invention what I claim and desire to secure by Letters-Patent is,

1. Tension mechanism for sewing machines comprising tension plates, a plurality of springs for yieldingly pressing said plates toward each other, and means operated by the separation of said plates for successively bringing said springs into effective action.

2. Tension mechanism for sewing machines comprising separable tension plates, yielding means tending at all times to hold said plates together, a movable member yieldingly pressed against an abutment, and a stop on said movable member adapted to be engaged after a fixed opening movement of said plates, whereby the yielding pressure on said movable member will resist the further opening movement.

3. Tension mechanism for sewing machines comprising separable tension plates, yielding means tending at all times to hold said plates together, a bushing passing through said plates, a stop on said bushing against which one of said plates strikes when they separate a predetermined amoimt, and yielding means for permitting said bushing to move when struck by said plate.

4. Tension mechanism for sewing machines comprising separable tension plates, a bushing passing through said plates, a stop on said bushing against which one of said plates strikes when they separate a predetermined amount, a shaft or spindle passingthrough said bushing connected to one of said plates, a spring connected to said shaft tending to so move it as to hold said plates together, and a spring engaging said bushing and adapted to resist its movement when struck by said plate.

5. The combination with a plate, of a hollow bushing passing through said plate and having a stop limiting its inward movement, a leaf spring on said plate engaging said bushing and tending to pull it inward, tension plates threaded on said bushing in front plates together and to resist their separation of said face plate, a flange on the end of on said bushing. 10 said bushing slightly separated from said In testimony whereof I afiix my signature plates when pressed together, a shaft passin presence of two Witnesses.

ing through said bushing and connected to RICHARD K. HOHMANN. the outer tension plate around said flange, Witnesses:

and a spring for pulling said shaft inward JOHN M. Corr,

through said bushing so as to press said B. C. RUST.

Copies of this patent may he obtained for five cents each, by addressing the Commissioner of ratentl. Washington, .D. 0. 

